Input system based on a three-dimensional inertial navigation system and trajectory estimation method thereof

ABSTRACT

An input system based on a three-dimensional inertial navigation system and a trajectory estimation method thereof is disclosed. The input system based on the three-dimensional inertial navigation system according to the present invention has acceleration sensors for outputting acceleration information just before motions, acceleration information on the motions, and acceleration information just after the motions; a rotation angle information estimation-computing portion for estimating rotation angle information on the motions through a predetermined computing process based on the outputted acceleration information just before the motions and acceleration information just after the motions; a conversion-computing unit for calculating position information on the motions based on the estimated rotation angle information on the motions and the outputted acceleration information on the motions; and an optimal plane-computing unit for projecting the position information on the motions onto an optimal plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of Korean Patent ApplicationNo. 2003-16779, filed on Mar. 13, 2003, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] An apparatus consistent with the present invention relates to aninput system based on a three-dimensional inertial navigation system anda trajectory estimation method thereof.

[0004] 2. Description of the Related Art

[0005] With progress in the information age, it is more frequentlydemanded to access and produce information anytime and anywhere, ratherthan a specific space in computers-equipped environments. Such demandsare satisfied with personal portable devices that have been developedand are widely spread, but further research is still required on inputsystems suitable for such personal portable devices. The specificationsrequired for the input system for personal portable devices include aneasy-to-carry and easy-to-input device, thus, there is a demand todevelop an input system that is smaller than personal portable devicesas well as being easy-to-carry. Further, the nature of the personalportable devices is to facilitate the inputs of new data anytime andanywhere, so that an input system is required which enables users toinput such data as they naturally write. In particular, if such an inputsystem can recover writing motions as naturally done on a general plane,a free space, or a sheet of paper so as to enable users to inputcharacters, graphics, gestures, and so on, the input system can beutilized as an excellent input system since it is excellent in theaspect of “universal purpose” and also does not require a particularlearning course for use.

[0006] Accordingly, in order to meet the demands on the input system asdescribed above, an input system has been proposed that can input datain space using the concept of a three-dimensional inertial navigationsystem.

[0007] The three-dimensional inertial navigation system refers to asystem that detects three-axis acceleration information and three-axisangular velocity information and applies the detected information to amoving object in order to estimate positions and attitudes of the movingobject in the three-dimensional space. The three-dimensional inertialnavigation system calculates the attitudes of the object and correctsthe acceleration information using an integral value of angular velocityinformation estimation values, accordingly, calculates velocityinformation by integrating the corrected acceleration information once,and calculates position information by integrating the correctedacceleration information twice.

[0008]FIG. 1 is a block diagram illustrating an input system using aconventional inertial navigation system.

[0009] The input system using the conventional inertial navigationsystem includes an input part 10 and a host device 20.

[0010] The host device 20 displays an image corresponding to motionsbased on the motions from the input part 10.

[0011] The input part 10 includes acceleration sensors 11, angularvelocity sensors 12, a rotation angle information-computing unit 13,conversion-computing unit 14, and a transmission unit 15.

[0012] The acceleration sensors 11 generate acceleration informationA_(b)(A_(bx), A_(by), A_(bz)) corresponding to motions based on themotions of the input part 10, and output the same to theconversion-computing unit 14. The subscript b in the accelerationinformation denotes acceleration information for a body frame of theinput part and the subscripts x, y, and z denote information on x-axis,y-axis, and z-axis.

[0013] The angular velocity sensors 12 generate angular velocityinformation W_(b)(W_(bx), W_(by), W_(bz)) corresponding to motions basedon the motions of the input part 10, and output the same to the rotationangle information-computing unit 13. The subscript b of the angularvelocity information denotes angular velocity information for the bodyframe of the input part, and the subscripts x, y, and z denoteinformation on x-axis, y-axis, and z-axis.

[0014] The rotation angle information-computing unit 13 inputs angularvelocity information from the angular velocity sensors 12. The inputtedangular velocity information is converted into rotation angleinformation χ(Φ, θ, ψ) through a predetermined computing process. Thepredetermined computing process for the conversion into the rotationangle information is well known to those skilled in the art, so adetailed description on the process will be omitted in the disclosure.

[0015] The conversion-computing unit 14 inputs acceleration informationand rotation angle information. The conversion-computing unit 14calculates the attitudes of the input part 10 based on the rotationangle information, corrects the acceleration information based on therotation angle information, calculates velocity information byintegrating the corrected acceleration information once, and calculatesposition information by integrating the corrected accelerationinformation twice. Such calculations can be performed based on Equations1, 2, and 3 as follows.

[0016] Prior to explanations of the following Equations, definitions aremade for terms used in the Equations as follows:

[0017] A body frame is a frame from which acceleration information andangular velocity information can be detected in correspondence to actualmotions of the input part 10.

[0018] A navigation frame is a reference frame for calculatinginformation applicable for a host device 20 by applying predeterminedcomputing matrices based on a result detected from the body frame.Herein, the coordinate axes for the navigation frame are referred to asX₀, Y₀, and Z₀.

[0019] Rotation angle information is as follows: The coordinate axes forthe navigation frame and the body frame coincide with each other whenthere is no rotation at an initial time. When the navigation frame andthe body frame coincide with each other at the initial time and thecoordinate axes for the body frame are referred to as X₀, Y₀, and Z₀, Ψdenotes the rotation angle information for the Z₀ axis. Further, θdenotes rotation angle information for a Y₁ axis indicating an axisafter the Y₀ axis is rotated as much as Ψ. Φ denotes rotation angleinformation for a X₂ axis indicating an axis after the X₀ axis isrotated as much as Ψ and θ, respectively.

[0020] A 3×3 matrix for converting a vector in the body frame into avector in the navigation frame is as follows:${C_{b}^{n}(\chi)} = \begin{bmatrix}{\theta_{c}\Psi_{c}} & {{{- \varphi_{c}}\Psi_{s}} + {\varphi_{s}\theta_{s}\Psi_{c}}} & {{\varphi_{s}\Psi_{s}} + {\varphi_{c}\theta_{s}\Psi_{c}}} \\{\theta_{c}\Psi_{s}} & {{\varphi_{c}\Psi_{c}} + {\phi_{s}\theta_{s}\Psi_{s}}} & {{{- \varphi_{s}}\Psi_{c}} + {\varphi_{c}\theta_{s}\Psi_{s}}} \\{- \theta_{s}} & {\varphi_{s}\theta_{c}} & {\varphi_{c}\theta_{c}}\end{bmatrix}$

[0021] In here, the subscripts s, c, and t stand for sine, cosine, andtangent functions, respectively, and the χ denotes rotation angleinformation in a 3×1 matrix.

[0022] The following is a matrix for calculating the rotation angleinformation based on the angular velocity information in the body frame:${R(\chi)} = \begin{bmatrix}1 & {\varphi_{s}\theta_{t}} & {\varphi_{c}\theta_{t}} \\0 & \varphi_{c} & {- \varphi_{s}} \\0 & {\varphi_{s}/\theta_{c}} & {\varphi_{c}/\theta_{c}}\end{bmatrix}$

[0023] Here, the subscripts s, c, and t stand for sine, cosine, andtangent functions, respectively, and the χ denotes the rotation angleinformation in a 3×1 matrix.

[0024] If the A_(b) denotes the acceleration information in the bodyframe, the W_(b) denotes the angular velocity information in the bodyframe, R denotes a matrix for calculating the rotation angle informationbased on the angular velocity information in the body frame, G is thegravitational acceleration, and the C_(b) ^(n) denotes a matrix forconverting a vector in the body frame into a vector in the navigationframe, position information in the navigation frame is P_(n), velocityinformation in the navigation frame is V_(n), and the rotation angleinformation is χ. These variables can be expressed in Equations 1, 2,and 3 as follows:

dP_(n)=V_(n)  [Equation 1]

dV _(n) =C _(b) ^(n)(χ)A _(b) −G  [Equation 2]

dχ=R(χ)W_(b)  [Equation 3]

[0025] Here, P_(n), V_(n), A_(b), G, and W_(b) are a 3×1 matrix,respectively, G is a matrix of [0,0, g]^(T), and dP_(n), dV_(n), and dχdenotes differentiations of P_(n), V_(n), and χ with respect to time,respectively.

[0026] Accordingly, the acceleration information and the angularvelocity information for the body frame outputted from the accelerationsensors and the angular velocity sensors respectively are computed andconverted into velocity information and position information for thenavigation frame, and a motion image corresponding to motions in thethree-dimensional space based on the conversion-computed positioninformation is projected to an optimal projection plane, and thenoutputted to the transmission unit 15.

[0027] The transmission unit 15 outputs the projected positioninformation to the host device 20.

[0028] By the above fashion, the motions of the input part 10 aredisplayed on the host device 20.

[0029] However, with both the acceleration sensors and the angularvelocity sensors used as above, the input part becomes heavy, whichbrings out a drawback that it is not suitable for portability. Also,there is a drawback in that the price of the angular velocity sensors isso high that the input parts using them become expensive. Further, thereexists a drawback in that an amount of power consumption becomes largesince the angular velocity sensors and the acceleration sensors have tobe all driven. Furthermore, there exists troublesomeness in that acorrection job has to be performed in case that the input part isequipped with the angular velocity sensors since the use of the angularvelocity sensors inevitably requires an initial correction job.

SUMMARY OF THE INVENTION

[0030] Illustrative, non-limiting embodiments of the present inventionovercome the above disadvantages and other disadvantages not describedabove. Also, the present invention is not required to overcome thedisadvantages described above, and an illustrative, non-limitingembodiment of the present invention may not overcome any of the problemsdiscussed above.

[0031] An apparatus consistent with the present invention provides aninput system based on a three-dimensional inertial navigation system anda trajectory estimation method thereof, capable of recovering motions inthe three-dimensional space by using only three acceleration sensorswithout any angular velocity sensor, that is, without using both threeacceleration sensors and three angular velocity sensors as in thethree-dimensional inertial navigation system.

[0032] The above aspect is achieved by providing an input system basedon a three-dimensional inertial navigation system and having an inputpart and a host device, which detects motion position informationcorresponding to three-dimensional motions of the input part and outputsthe detected motion position information to the host device. The inputsystem comprises acceleration sensors for outputting accelerationinformation just before the motions (hereinafter, referred to aspre-motion acceleration information where applicable), accelerationinformation on the motions (hereinafter, referred to as motionacceleration information where applicable), and acceleration informationjust after the motions (hereinafter, referred to as post-motionacceleration information where applicable); a rotation angle informationestimation-computing portion for estimating rotation angle informationΦ, θ, and Ψ on the motions (hereinafter, referred to as motion rotationangle information where applicable) through a predetermined computingprocess based on the outputted pre-motion acceleration information andpost-motion acceleration information; a conversion-computing unit forcalculating the motion position information based on the estimatedmotion rotation angle information and the outputted motion accelerationinformation; and an optimal plane-computing unit for projecting themotion position information onto an optimal plane.

[0033] The rotation angle information estimation-computing portionincludes a first computing unit for calculating rotation angleinformation Φ1, θ1, and Ψ1 just before the motions (hereinafter,referred to as pre-motion rotation angle information where applicable)and rotation angle information Φ2, θ2, and Ψ2 just after the motions(hereinafter, referred to as post-motion rotation angle informationwhere applicable) through a predetermined computing process based on theoutputted pre-motion acceleration information and post-motionacceleration information; and a second computing unit for calculatingthe motion rotation angle information through a predetermined computingprocess based on the calculated pre-motion rotation angle informationand post-motion rotation angle information.

[0034] Preferably, in the first computing unit, the pre-motion rotationangle information Φ1 and the post-motion rotation angle information Φ2become ${\Phi 1} = {\tan^{- 1}\left( \frac{A_{by1}}{A_{bz1}} \right)}$

[0035] and${{\Phi 2} = {\tan^{- 1}\left( \frac{A_{by2}}{A_{bz2}} \right)}},$

[0036] respectively, and, here, if coordinate axes of a body frame ofthe input part are denoted as X, Y, and Z, A_(by1) and A_(by2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Y axis respectively, and A_(bz1) and A_(bz2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Z axis respectively, and, if coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote thepre-motion rotation angle information and the post-motion rotation angleinformation for the Z₀ axis, and θ1 denotes the pre-motion rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ1, θ2 denotes the post-motion rotation angleinformation for Y₁ axis indicating an axis after the Y₀ axis is rotatedas much as Ψ2, Φ1 denotes the pre-motion rotation angle information forthe X₂ indicating an axis after the X₀ axis is rotated as much as Ψ1 andθ1, respectively, and Φ2 denotes the pre-motion rotation angleinformation for the X₂ axis indicating an axis after the X₀ is rotatedas much as Ψ2 and θ2, respectively.

[0037] Preferably, in the first computing unit, the pre-motion rotationangle information θ1 and the post-motion rotation angle information θ2become${\theta 1} = {\tan^{- 1}\left( \frac{A_{bx1}}{\sqrt{A_{by1}^{2} + A_{bz1}^{2}}} \right)}$

[0038] and${{\theta 2} = {\tan^{- 1}\left( \frac{A_{bx2}}{\sqrt{A_{by2}^{2} + A_{bz2}^{2}}} \right)}},$

[0039] respectively, and, here, if coordinate axes of a body frame ofthe input part are denoted as X, Y, and Z, A_(bx1) and A_(bx2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the X axis respectively, and A_(by1) and A_(by2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Y axis respectively, and A_(bz1) and A_(bz2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Z axis respectively, and, if coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote thepre-motion rotation angle information and the post-motion rotation angleinformation for the Z₀ axis, and θ1 denotes the pre-motion rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ1, and θ2 denotes the post-motion rotation angleinformation for Y₁ axis indicating an axis after the Y₀ axis is rotatedas much as Ψ2.

[0040] Preferably, in the second computing unit, the motion rotationangle information d) becomes Φ(t)=a*t+b, and, here, if t₁ denotes timejust before the motions, t₂ denotes time just after the motions, adenotes [Φ(t₂)−(t₁)]/(t₂−t₁), b denotes−a*t, +Φ(t₁), and coordinate axesfor the navigation frame are denoted as X₀, Y₀, and Z₀, the Ψ denotesthe rotation angle information for the Z₀ axis, the θ denotes therotation angle information for the Y₁ axis indicating an axis after theY₀ axis is rotated as much as Ψ, and the Φ denotes the rotation angleinformation for the X₂ axis indicating an axis after the X₀ axis isrotated as much as Ψ and θ, respectively.

[0041] Preferably, in the second computing unit, the motion rotationangle information θ becomes θ(t)=c*t+d, and, here, if t₁ denotes timejust before the motions, t₂ denotes time just after the motions, cdenotes [θ(t₂)−θ(t₁)]/(t₂−t₁), d denotes−c*t₁+θ(t₁), and coordinate axesare denoted as X₀, Y₀, and Z₀, the Ψ denotes the rotation angleinformation for the Z₀ axis and the 0 denotes the rotation angleinformation for the Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ.

[0042] Further, the above object is achieved by providing the inputsystem based on the three-dimensional inertial navigation systemaccording to the present invention and having an input part and a hostdevice, which detects motion position information corresponding tothree-dimensional motions of the input part and outputs the detectedmotion position information to the host device. The input systemcomprises acceleration sensors for outputting motion accelerationinformation; a rotation angle information estimation-computing portionfor estimating motion rotation angle information Φ, θ, and Ψ based onacceleration information based on the gravitational accelerationseparated from the outputted motion acceleration information; aconversion-computing unit for calculating motion position informationbased on the estimated motion rotation angle information and theoutputted motion acceleration information; and an optimalplane-computing unit for projecting the motion position information ontoan optimal plane.

[0043] The rotation angle information estimation-computing portionincludes a separation unit for separating acceleration information basedon the motions of the input part itself and acceleration informationbased on the gravitational acceleration from the outputted motionacceleration information based on a predetermined process; and acomputing unit for calculating the motion rotation angle informationthrough the predetermined computing process based on the accelerationinformation based on the separated gravitational acceleration.

[0044] Preferably, but not necessarily, the predetermined process forseparating the acceleration information based on the gravitationalacceleration from the motion acceleration information is to pass themotion acceleration information through a low-pass filter.

[0045] Preferably, but not necessarily, in the computing unit, themotion rotation angle information Φ becomes${\Phi = {\tan^{- 1}\left( \frac{A_{by}}{A_{bz}} \right)}},$

[0046] and, here, if coordinate axes of a body frame of the input partare denoted as X, Y, and Z, A_(by) denotes acceleration information forthe Y axis and A_(bz) denotes acceleration information for the Z axis,and, if coordinate axes for a navigation frame are denoted as X₀, Y₀,and Z₀, Ψ denotes rotation angle information for the Z₀ axis, θ denotesrotation angle information for a Y₁ axis indicating an axis after the Y₀axis is rotated as much as Ψ, and Φ denotes rotation angle informationfor an X₂ indicating an axis after the X₀ is rotated as much as Ψ and θ,respectively.

[0047] Preferably, but not necessarily, in the computing unit, themotion rotation angle information θ becomes${\theta = {\tan^{- 1}\left( \frac{A_{bx}}{\sqrt{A_{by}^{2} + A_{bz}^{2}}} \right)}},$

[0048] and, here, if coordinate axes for the body frame are denoted asX, Y, and Z, A_(bx) denotes acceleration information for the X axis,A_(by) denotes acceleration information for the Y axis, A_(bz) denotesacceleration information for the Z axis, and coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ denotes rotation angleinformation for the Z₀ axis and θ denotes rotation angle information fora Y₁ axis indicating an axis after the Y₀ is rotated as much as Ψ.

[0049] Further, the above object is achieved by providing a trajectoryestimation method for an input system based on a three-dimensionalinertial navigation system and having an input part and a host deviceaccording to the present invention, which detects motion positioninformation corresponding to three-dimensional motions of the input partand outputs the detected motion position information to the host device.The method comprises steps of (a) outputting motion accelerationinformation, pre-motion acceleration information, and post-motionacceleration information just after the motions; (b) estimating motionrotation angle information Φ, θ, and Ψ through a predetermined computingprocess based on the outputted pre-motion acceleration information andpost-motion acceleration information; (c) calculating the motionposition information based on the estimated motion rotation angleinformation and the outputted motion acceleration information; and (d)projecting the motion position information onto an optimal plane.

[0050] The step (b) includes steps of (b1) calculating pre-motionrotation angle information Φ1, θ1, and Ψ1 and post-motion rotation angleinformation Φ2, θ2, and Ψ2 through a predetermined computing processbased on the outputted pre-motion acceleration information andpost-motion acceleration information; and (b2) calculating the motionrotation angle information through a predetermined computing processbased on the calculated pre-motion rotation angle information andpost-motion rotation angle information.

[0051] Preferably, but not necessarily, in the step (b1), the pre-motionrotation angle information Φ1 and the post-motion rotation angleinformation Φ2 become${\Phi 1} = {{{\tan^{- 1}\left( \frac{A_{by1}}{A_{bz1}} \right)}\quad {and}\quad {\Phi 2}} = {\tan^{- 1}\left( \frac{A_{by2}}{A_{bz2}} \right)}}$

[0052] respectively, and, here, if coordinate axes of a body frame ofthe input part are denoted as X, Y, and Z, A_(by1) and A_(by2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Y axis respectively, and A_(bz1) and A_(bz2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Z axis respectively, and, if coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote thepre-motion rotation angle information and the post-motion rotation angleinformation for the Z₀ axis, and θ1 denotes the pre-motion rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ1, θ2 denotes the post-motion rotation angleinformation for Y₁ axis indicating an axis after the Y₀ axis is rotatedas much as Ψ2, Φ1 denotes the pre-motion rotation angle information forthe X₂ indicating an axis after the X₀ axis is rotated as much as Ψ1 andθ1, respectively, and Φ2 denotes the pre-motion rotation angleinformation for the X₂ axis indicating an axis after the X₀ is rotatedas much as Ψ1, θ2, respectively.

[0053] Preferably, but not necessarily, in the step (b1), the pre-motionrotation angle information θ1 and the post-motion rotation angleinformation θ2 become${{\theta 1} = {{{\tan^{- 1}\left( \frac{A_{bx1}}{\sqrt{A_{by1}^{2} + A_{bz1}^{2}}} \right)}\quad {and}\quad {\theta 2}} = {\tan^{- 1}\left( \frac{A_{bx2}}{\sqrt{A_{by2}^{2} + A_{bz2}^{2}}} \right)}}},$

[0054] respectively, and, here, if coordinate axes of a body frame ofthe input part are denoted as X, Y, and Z, A_(bx1) and A_(bx2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the X axis respectively, and A_(by1) and A_(by2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Y axis respectively, and A_(bz1) and A_(bz2) denotethe pre-motion acceleration information and the post-motion accelerationinformation for the Z axis respectively, and, if coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote thepre-motion rotation angle information and the post-motion rotation angleinformation for the Z₀ axis, and θ1 denotes the pre-motion rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ1, and θ2 denotes the post-motion rotation angleinformation for Y₁ axis indicating an axis after the Y₀ axis is rotatedas much as Ψ2.

[0055] Preferably, but not necessarily, in the step (b2), the motionrotation angle information Φ becomes Φ(t)=a*t+b and, here, if t₁ denotestime just before the motions, t₂ denotes time just after the motions, adenotes [Φ(t₂)−Φ(t₁)]/(t₂−t₁), b denotes −a*t, +Φ(t₁), and coordinateaxes are denoted as X₀, Y₀, and Z₀, the Ψ denotes the rotation angleinformation for the Z₀ axis, the θ denotes the rotation angleinformation for the Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ, and the Φ denotes the rotation angle informationfor the X₂ axis indicating an axis after the X₀ axis is rotated as muchas Ψ and θ, respectively.

[0056] Preferably, but not necessarily, in the step (b2), the motionrotation angle information θ becomes θ(t)=c*t+d and, here, if t₁ denotestime just before the motions, t₂ denotes time just after the motions, cdenotes [θ(t₂)−θ(t₁)]/(t₂−t₁), d denotes −c*t, +θ(t₁), and coordinateaxes are denoted as X₀, Y₀, and Z₀, the Ψ denotes the rotation angleinformation for the Z₀ axis and the 0 denotes the rotation angleinformation for the Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ.

[0057] Further, the above object is achieved by providing a trajectoryestimation method for an input system based on a three-dimensionalinertial navigation system and having an input part and a host device,which detects motion position information corresponding to motions ofthe input part based on three-dimensional motions of the input part andoutputs the detected motion position information to the host device. Themethod comprises steps of: (a) outputting motion accelerationinformation; (b) estimating motion rotation angle information Φ, θ, andΨ based on acceleration information based on the gravitationalacceleration separated from the outputted motion accelerationinformation; (c) calculating motion position information based on theestimated motion rotation angle information and the outputted motionacceleration information; and (d) projecting the motion positioninformation onto an optimal plane.

[0058] The step (b) includes steps of (b1) separating accelerationinformation based on the motions of the input part itself andacceleration information based on the gravitational acceleration fromthe outputted motion acceleration information based on a predeterminedprocess; and (b2) calculating the motion rotation angle informationthrough the predetermined computing process based on the accelerationinformation based on the separated gravitational acceleration.

[0059] Preferably, but not necessarily, the predetermined process in thestep (b1) is to pass the motion acceleration information through alow-pass filter.

[0060] Preferably, but not necessarily, the motion rotation angleinformation 4 in the step (b2) becomes$\Phi = {\tan^{- 1}\left( \frac{A_{by}}{A_{bz}} \right)}$

[0061] and, here, if coordinate axes of a body frame of the input partare denoted as X, Y, and Z, A_(by) denotes acceleration information forthe Y axis and A_(bz) denotes acceleration information for the Z axis,and, if coordinate axes for a navigation frame are denoted as X₀, Y₀,and Z₀, Ψ denotes rotation angle information for the Z₀ axis, θ denotesrotation angle information for a Y₁ axis indicating an axis after the Y₀axis is rotated as much as Ψ, and Φ denotes rotation angle informationfor an X₂ indicating an axis after the X₀ is rotated as much as Ψ and 0,respectively.

[0062] Preferably, but not necessarily, the motion rotation angleinformation θ in the step (b2) becomes$\theta = {\tan^{- 1}\left( \frac{A_{bx}}{\sqrt{A_{by}^{2} + A_{bz}^{2}}} \right)}$

[0063] and, here, if coordinate axes for the body frame are denoted asX, Y, and Z, A_(bx) denotes acceleration information for the X axis,A_(by) denotes acceleration information for the Y axis, A_(bz) denotesacceleration information for the Z axis, and coordinate axes for thenavigation frame are denoted as X₀, Y₀, and Z₀, Ψ denotes rotation angleinformation for the Z₀ axis and θ denotes rotation angle information fora Y₁ axis indicating an axis after the Y₀ is as much as Ψ.

[0064] Accordingly, the present invention can recover thethree-dimensional motions by using only the three acceleration sensorswithout the angular velocity sensors in the three-dimensional inertialnavigation system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The features and advantages of the present invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the following drawings in which like reference numeralsrefer to like elements, and wherein:

[0066]FIG. 1 is a block diagram for showing an input system using aconventional inertial navigation system;

[0067]FIG. 2 is a block diagram for showing an input system including aninput part equipped with a rotation angle informationestimation-computing portion according to an embodiment of the presentinvention;

[0068]FIG. 3 is a block diagram for showing an input system including aninput part equipped with a rotation angle informationestimation-computing portion according to another embodiment of thepresent invention;

[0069]FIG. 4A is a graph for showing acceleration information on motionsoutputted from acceleration sensors;

[0070]FIG. 4B is a graph for showing acceleration information in casethat only the acceleration information based on the gravitationalacceleration is separated from the acceleration information of FIG. 4Awhen a low-pass filter is provided in a separation unit;

[0071]FIG. 5 is a flow chart for showing a trajectory estimation methodfor an input system of FIG. 2 according to an embodiment of the presentinvention;

[0072]FIG. 6 is a flow chart for showing a trajectory estimation methodfor an input system of FIG. 3 according to another embodiment of thepresent invention;

[0073]FIG. 7A is a view for showing results of certain numbers writtenby an input system to which the present invention is applied;

[0074]FIG. 7B is a view for showing results of other certain numberswritten by an input system to which the present invention is applied;and

[0075]FIG. 7C is a view for showing results of certain letters writtenby an input system to which the present invention is applied.

DETAILED DESCRIPTION OF ILLUSTRATIVE, NON-LIMITING EMBODIMENTS OF THEINVENTION

[0076] Hereinafter, an input system according to an exemplary embodimentof the present invention is described in detail with reference to theaccompanying drawings.

[0077]FIG. 2 is a block diagram for showing an input system including aninput part 100 equipped with a rotation angle informationestimation-computing portion 120 according to an embodiment of thepresent invention.

[0078] The input system according to the present invention has the inputpart 100 and a host device 300.

[0079] The input part 100 includes acceleration sensors 110, therotation angle information estimation-computing portion 120, aconversion-computing unit 130, an optimal plane-computing unit 135 and atransmission unit 140.

[0080] The acceleration sensors 110 are provided for three X, Y₁ and Zaxes of a body frame of the input part 100 according to three x, y, andz axes to be based on motions of the input part 100. The accelerationsensors 110 detect and output acceleration information on motions(hereinafter, referred to as motion acceleration information whereapplicable), acceleration information just before the motions(hereinafter, referred to as pre-motion acceleration information whereapplicable), and acceleration information just after the motions(hereinafter, referred to as post-motion acceleration information whereapplicable), respectively. It is preferable for the three accelerationsensors to be provided in the input part 100, but it is possible toprovide two acceleration sensors that can detect accelerationinformation on two axes.

[0081] Definitions for the acceleration information on motions,acceleration information just before the motions, and accelerationinformation just after the motions, are as follows.

[0082] In order to do trajectory estimations for the input part 100according to an embodiment of FIG. 2, an assumption is necessary thatthe input part 100 has to remain still just before and after intendedmotions to be taken by the input part 100. Accordingly, the accelerationsensors 110 according to the present invention can detect accelerationinformation just before and after intended motions to be taken by theinput part 100. The pre-motion acceleration information refers toacceleration information just before intended motions. Further, thepost-motion acceleration information refers to acceleration informationjust after intended motions. Motion acceleration information refers toacceleration information based on intended motions to be taken by auser.

[0083] The rotation angle information estimation-computing portion 120computes and estimates rotation angle information based on pre-motionacceleration information and post-motion acceleration informationoutputted from the acceleration sensors 110.

[0084] The rotation angle information estimation-computing portion 120according to an embodiment of the present invention includes a firstcomputing unit 121 and a second computing unit 122.

[0085] The first computing-unit 121 inputs pre-motion accelerationinformation and post-motion acceleration information on the input part100 from the acceleration sensors 110.

[0086] The first computing unit 121 computes Φ and θ of rotation angleinformation just before motions through a predetermined computingprocess based on pre-motion acceleration information. Here, the rotationangle information just before motions is pre-motion rotation angleinformation corresponding to the pre-motion acceleration information.

[0087] The first computing unit 121 computes Φ and θ of rotation angleinformation just after motions through a predetermined computing processbased on post-motion acceleration information. In here, the rotationangle information just after motions is post-motion rotation angleinformation corresponding to the post-motion acceleration information.

[0088] In case that coordinate axes for the body frame are denoted as X,Y, and Z, acceleration information for the X axis of the body frame isdenoted as A_(bx), acceleration information for the Y axis of the bodyframe as A_(by), acceleration information for the Z axis of the bodyframe as A_(bz), rotation angle information for a Z₀ axis as ψ, androtation angle information for a Y₁ axis, indicating an axis after a Y₀axis is rotated as much as Ψ, as θ, Equation 4 expresses rotation angleinformation Φ for a X₂ axis indicating an axis after the X₀ axis isrotated as much as Ψ and θ, respectively. $\begin{matrix}{\Phi = {\tan^{- 1}\left( \frac{A_{by}}{A_{bz}} \right)}} & \left\lbrack {{Equation}\quad 4} \right\rbrack\end{matrix}$

[0089] In case that coordinate axes for the body frame are denoted as X,Y, and Z, acceleration information for the X axis of the body frame isdenoted as A_(bx), acceleration information for the Y axis of the bodyframe as A_(by), acceleration information for the Z axis of the bodyframe as A_(bz), and rotation angle information for a Z₀ axis as Ψ,rotation angle information θ for Y₁ axis indicating an axis after a Y₀axis is rotated as much as Ψ can be expressed in Equation 5 as follows:$\begin{matrix}{\theta = {\tan^{- 1}\left( \frac{A_{bx}}{\sqrt{A_{by}^{2} + A_{bz}^{2}}} \right)}} & \left\lbrack {{Equation}\quad 5} \right\rbrack\end{matrix}$

[0090] Equations 4 and 5 are formulae by which the Φ and θ of rotationangle information can be respectively calculated from accelerationinformation at the state of no motion.

[0091] The second computing unit 122 inputs the Φ and θ of pre-motionrotation angle information computed from the first computing unit 121.

[0092] The second computing unit 122 inputs the Φ and θ of post-motionrotation angle information computed from the first computing unit 121.

[0093] The second computing unit 122 computes the motion rotation angleinformation Φ through a predetermined computing process based on the Φof the inputted pre-motion rotation angle information and the Φ of theinputted post-motion rotation angle information.

[0094] The second computing unit 122 computes the motion rotation angleinformation θ through a predetermined computing process based on the θof the inputted pre-motion rotation angle information and the θ of theinputted post-motion rotation angle information.

[0095] If the time just before a motion is denoted as t₁, the time justafter a motion as t₂, [Φ(t₂)−Φ(t₁)]/(t₂−t₁) as a, and −a*t₁+Φ(t₁) as b,the Φ(t) of the motion rotation angle information can be expressed inEquation 6 as follows:

Φ(t)=a*t+b  [Equation 6]

[0096] Further, if the time just before a motion is denoted as t₁, thetime just after a motion as t₂, [θ(t₂)−θ(t₁)]/(t₂−t₁) as c, and−c*t₁+θ(t₁) as d, the θ(t) of the motion rotation angle information canbe expressed in Equation 7 as follows:

θ(t)=C*t+d  [Equation 7]

[0097] The conversion-computing unit 130 inputs motion accelerationinformation from the acceleration sensors 110, and inputs motionrotation angle information estimated from the rotation angle informationestimating-computing portion 120. Based on the inputted motionacceleration information and motion rotation angle information, motionvelocity information V_(n) and motion position information P_(n) for thenavigation frame are calculated as in the conversion-computing unit ofFIG. 1.

[0098] The optimal plane-computing unit 135 projects onto a virtualtwo-dimensional optimal plane the motion position information outputtedfrom the conversion-computing unit 130 to obtain coordinate values.

[0099] The transmission unit 140 outputs to the host device 300 theprojected position information outputted from the optimalplane-computing unit 135. The transmission unit 140 can be constructedwith a wired communication module, but, preferably, with a wirelesscommunication module such as Bluetooth®.

[0100] The host device 300 displays position information correspondingto motions based on the motions of the input part 100. The host device300 is preferably a personal portable device.

[0101]FIG. 3 is a block diagram for showing an input system includingthe input part 200 equipped with the rotation angle informationestimation-computing unit 120 according to another embodiment of thepresent invention.

[0102] As described in FIG. 2, the input system according to the presentinvention includes the host device 300 and the input part 200.

[0103] The input part 200 has acceleration sensors 210, a rotation angleinformation estimation-computing portion 220, a conversion-computingunit 230, an optimal plane-computing unit 235, and a transmission unit240.

[0104] The description on the conversion-computing unit 230 and thetransmission unit 240 is the same as in FIG. 2.

[0105] Accordingly, hereinafter, a description is made only of theacceleration sensors 210 and the rotation angle informationestimation-computing portion 220.

[0106] The acceleration sensors 210 according to the present embodimentdetect and output motion acceleration information. Differently from theembodiment of FIG. 2, there is no need to detect accelerationinformation just before and after motions.

[0107] The rotation angle information estimation-computing portion 220according to the present embodiment includes a separation unit 221 and acomputing unit 222.

[0108] The separation unit 221 inputs motion acceleration informationoutputted. Thus, the separation unit 221 separates accelerationinformation based on the motion of the input part 200 itself andacceleration information based on the gravitational acceleration fromthe inputted motion acceleration information through a predeterminedprocess.

[0109] For the predetermined process, it is preferable to provide alow-pass filter (LPF) to the separation unit 221.

[0110] In general, the acceleration information based on thegravitational acceleration exists in a lower frequency bandwidth thanthe acceleration information based on motions themselves. Accordingly,in case that a low-pass filter is provided to the separation unit 221,the acceleration information based on the gravitational acceleration isfiltered by the separation unit 221.

[0111] The computing unit 222 is inputted with acceleration informationbased on the gravitational acceleration.

[0112] The computing unit 222 calculates motion rotation angleinformation through Equations 4 and 5 based on acceleration informationbased on the gravitational acceleration.

[0113] In general, a stationary object has no motions and is affectedonly by the gravitational force, so that acceleration information basedon the gravitational acceleration of the motion acceleration informationcorresponds to a stationary state.

[0114] Further, as described above, Equations 4 and 5 can be appliedonly in a stationary state. Therefore, Equations 4 and 5 can be appliedto the acceleration information based on the gravitational acceleration.The computing unit 222 inputs the acceleration information based on thegravitational acceleration, and calculates motion rotation angleinformation through applications of Equations 4 and 5.

[0115] The calculated motion rotation angle information and the motionacceleration information outputted from the acceleration sensors 210 aretransmitted to the conversion-computing unit 230, and the motionposition information for the navigation frame calculated in theconversion-computing unit 230 is transmitted to the host device 300through the optimal plane-computing unit 135.

[0116] However, the present disclosure does not perform any estimationfor ψ. This is because the ψ itself does not affect the trajectoryrecovery for the input part. Therefore, the values for the ψ in the twoembodiments are set to zero.

[0117]FIG. 4A is a graph for showing motion acceleration informationoutputted from the acceleration sensors 110.

[0118] In general, motion acceleration information outputted from theacceleration sensors is composite information of accelerationinformation based on the gravitational acceleration and accelerationinformation based on motions themselves. As shown in FIG. 4A,acceleration information based on motions themselves generally exists ina frequency band ranging from 1 Hz to 20 Hz, and accelerationinformation based on the gravitational acceleration exists in afrequency band near 0 Hz.

[0119]FIG. 4B is a graph for showing acceleration information in casethat only the acceleration information based on the gravitationacceleration is separated from the acceleration information of FIG. 4Awith the separation unit 221 equipped with a low-pass filter.

[0120] In case that the separation unit 221 has a low-pass filter,acceleration information in a high-frequency band is not filtered for anoutput, but only the acceleration information in a low-frequency band isoutputted. Therefore, as shown in FIG. 4B, only the accelerationinformation based on the gravitational acceleration is outputted.

[0121]FIG. 5 is a flow chart for showing a trajectory estimation methodbased on the input system according to the embodiment of FIG. 2.

[0122] Descriptions are made of the method with reference to FIG. 2 andFIG. 5. First, a user takes certain motions with the input part 100. Theacceleration sensors 110 in the input part 100 detect and output motionacceleration information based on the motions of the input part 100(S400).

[0123] The outputted acceleration information consists of pre-motionacceleration information, motion acceleration information, andpost-motion acceleration information. The outputted pre-motion andpost-motion acceleration information is inputted to the rotation angleinformation estimation-computing portion 120. The first computing unit121 in the rotation angle information estimation-computing portion 120applies Equations 4 and 5 to the pre-motion acceleration information andthe post-motion acceleration information. Thus, pre-motion rotationangle information corresponding to the pre-motion accelerationinformation is calculated, and post-motion rotation angle informationcorresponding to the post-motion acceleration information is calculated(S410).

[0124] The calculated pre-motion rotation angle information and thepost-motion rotation angle information are outputted to the secondcomputing unit 122. The second computing unit 122 applies Equations 6and 7 to the pre-motion rotation angle information and the post-motionrotation angle information. Accordingly, the motion rotation angleinformation is calculated (S420).

[0125] The calculated motion rotation angle information is outputted tothe conversion-computing unit 130. Further, the acceleration informationoutputted from the acceleration sensors 110 is outputted to theconversion-computing unit 130. The conversion-computing unit 130calculates motion position information for the navigation frame based onthe inputted acceleration information and angular velocity information(S430).

[0126] The motion position information for the calculated navigationframe is projected onto an optimal plane by the optimal plane-computingunit 135 (S440). The position information projected on the optimal planeis outputted to the host device 300 through the transmission unit 140(S450).

[0127]FIG. 6 is a flow chart for showing a trajectory estimation methodfor the input system according to the embodiment of FIG. 3.

[0128] Descriptions are made with reference to FIG. 3 and FIG. 6. First,a user takes certain motions with the input part 200. The accelerationsensors 210 in the input part 200 outputs motion accelerationinformation based on the motions of the input part 200 (S500).

[0129] The outputted motion acceleration information consists ofacceleration information based on the motions themselves andacceleration information based on the gravitational acceleration. Theoutputted motion acceleration information is inputted to the rotationangle information estimation-computing portion 220. The separation unit221 in the rotation angle information estimation-computing portion 220separates the inputted motion acceleration information into theacceleration information based on the motions themselves and theacceleration information based on the gravitational acceleration (S510).

[0130] The acceleration information based on the separated gravitationalacceleration is inputted to the rotation angle informationestimation-computing portion 220. The computing unit 222 in the rotationangle information estimation-computing portion 220 applies Equations 4and 5 to the acceleration information based on the gravitationalacceleration of the separated acceleration information. Accordingly,motion rotation angle information is calculated (S520).

[0131] The calculated motion rotation angle information is outputted tothe conversion-computing unit 230. Further, the acceleration informationoutputted from the acceleration sensors 210 is outputted to theconversion-computing unit 230. The conversion-computing unit 230calculates motion position information for the navigation frame based onthe inputted acceleration information and angular velocity information(S530).

[0132] The calculated motion position information for the gravitationalframe is projected onto an optimal plane by the optimal plane-computingunit 235 (S540). The position information projected on the optimal planeis outputted to the host device 300 through the transmission unit 240(S550).

[0133]FIG. 7A illustrates results of certain numbers written by an inputapparatus to which the present invention is applied.

[0134]FIG. 7A shows the experimental results for numbers 0˜3.

[0135] The one-dotted lines in FIG. 7A indicate numbers written by aninput part without angular velocity sensors according to the embodimentof FIG. 2. The dotted lines in FIG. 7A indicate numbers written by theinput part without angular velocity sensors according to the embodimentof FIG. 3. The solid lines indicate numbers directly written on a tabletby a stylus pen. The two-dotted lines in FIG. 7A indicate numberswritten by an input part with angular velocity sensors.

[0136]FIG. 7B illustrates results of other certain numbers written bythe input part to which the present invention is applied, and FIG. 7Cillustrates results of certain letters written by the input part towhich the present invention is applied.

[0137]FIG. 7B shows an experimental result for numbers 6˜9, and FIG. 7Cshows an experimental result for English letters G, H, I, and J.

[0138] The descriptions on the one-dotted lines, dotted lines, solidlines, and two-dotted lines are the same as in FIG. 7A.

[0139] As shown in FIG. 7A, FIG. 7B, and FIG. 7C, the numbers andletters that are written by the input part with angular velocity sensorsand directly written on the tablet are nearly the same as those that arewritten by the input parts according to the embodiments of the presentinvention, and, further, it can be seen that the degrees to which thewritings can be recognized are nearly the same

[0140] However, the embodiment presented in FIG. 2 and the embodimentpresent in FIG. 3 are each structured to perform a predeterminedcomputing process in the input part so that only the positioninformation as final processing result values is transmitted to the hostdevice.

[0141] However, the above structure is exemplified for the aboveembodiments, and, for a different embodiment, the structure may beconstructed in a different way in order that the input part detects onlyacceleration information outputted from the acceleration sensors, thedetected acceleration information is transmitted to the host devicethrough the transmission unit, and the host device performs thecomputing process by the rotation angle information estimation-computingportion, the computing process by the conversion-computing unit, and theoptimal plane-computing process.

[0142] Further, for another embodiment, the structure may be constructedso that the input part detects acceleration information outputted fromthe acceleration sensors, the rotation angle informationestimation-computing portion calculates rotation angle information basedon the detected acceleration information, the calculated rotation angleinformation is transmitted to the host device through the transmissionunit, and the host device performs the computing process by theconversion-computing unit and the optimal plane-computing process.

[0143] The input system based on the three-dimensional inertialnavigation system and a trajectory estimation method thereof accordingto the present invention can recover three-dimensional motions in use ofonly three acceleration sensors without angular velocity sensors, ratherthan using three acceleration sensors and three angular velocity sensorsas in the three-dimensional inertial navigation system. Further, thepresent invention can input any writings a user desires without limit toa time and place. Accordingly, the input system can be manufactured at alow cost since only three acceleration sensors are used, manufacturedlight-weight to be convenient in carrying, reduce power consumption, andeliminate the troublesomeness of initial correction work.

[0144] While the invention has been shown and described with referenceto exemplary embodiments thereof for illustrative purposes, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims.

What is claimed is:
 1. An input system based on a three-dimensionalinertial navigation system and having an input part and a host device,and for detecting motion position information corresponding tothree-dimensional motions of the input part and outputting the detectedmotion position information to the host device, comprising: accelerationsensors for outputting pre-motion acceleration information, motionacceleration information, and post-motion acceleration information; arotation angle information estimation-computing portion for estimatingmotion rotation angle information Φ, θ, and Ψ through a predeterminedcomputing process based on the outputted pre-motion accelerationinformation and post-motion acceleration information; aconversion-computing unit for calculating the motion positioninformation based on the estimated motion rotation angle information andthe outputted motion acceleration information; and an optimalplane-computing unit for projecting the motion position information ontoan optimal plane.
 2. The input system as claimed in claim 1, wherein therotation angle information estimation-computing portion includes: afirst computing unit for calculating pre-motion rotation angleinformation Φ1, θ1, and Ψ1 and post-motion rotation angle informationΦ2, θ2, and Ψ2 through a predetermined computing process based on theoutputted pre-motion acceleration information and post-motionacceleration information; and a second computing unit for calculatingthe motion rotation angle information through a predetermined computingprocess based on the calculated pre-motion rotation angle informationand post-motion rotation angle information.
 3. The input system asclaimed in claim 2, wherein the first computing unit calculates thepre-motion rotation angle information Φ1 and the post-motion rotationangle information Φ2 based on equations as follows: $\begin{matrix}{{{\Phi 1} = {\tan^{- 1}\left( \frac{A_{by1}}{A_{bz1}} \right)}};} \\{{\Phi 2} = {\tan^{- 1}\left( \frac{A_{by2}}{A_{bz2}} \right)}}\end{matrix}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(by1) and A_(by2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Y axis,respectively, and A_(bz1) and A_(bz2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Z axis,respectively, and, if coordinate axes for a navigation frame are denotedas X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote the pre-motion rotation angleinformation and the post-motion rotation angle information for the Z₀axis, and θ1 denotes the pre-motion rotation angle information for a Y₁axis indicating an axis after the Y₀ axis is rotated as much as Ψ1, θ2denotes the post-motion rotation angle information for Y₁ axisindicating an axis after the Y₀ axis is rotated as much Ψ2, Φ1 denotesthe pre-motion rotation angle information for the X₂ indicating an axisafter the X₀ axis is rotated as much as Ψ1 and θ1, respectively, and Φ2denotes the pre-motion rotation angle information for the X₂ axisindicating an axis after the X₀ is rotated as much as Ψ2 and θ2,respectively.
 4. The input system as claimed in claim 2, wherein thefirst computing unit calculates the pre-motion rotation angleinformation θ1 and the post-motion rotation angle information θ2 basedon equations as follows: $\begin{matrix}{{{\theta \quad 1} = {\tan^{- 1}\left( \frac{A_{bx1}}{\sqrt{A_{by1}^{2} + A_{bz1}^{2}}} \right)}},} \\{{\theta \quad 2} = {\tan^{- 1}\left( \frac{A_{bx2}}{\sqrt{A_{by2}^{2} + A_{bz2}^{2}}} \right)}}\end{matrix}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(bx1) and A_(bx2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the X axis,respectively, and A_(by1) and A_(by2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Y axis,respectively, and A_(bz1) and A_(bz2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Z axis,respectively, and, if coordinate axes for a navigation frame are denotedas X₀, Y₀, and Z₀, Ψ 1 and Ψ2 denote the pre-motion rotation angleinformation and the post-motion rotation angle information for the Z₀axis, and θ1 denotes the pre-motion rotation angle information for a Y₁axis indicating an axis after the Y₀ axis is rotated as much as Ψ1, andθ2 denotes the post-motion rotation angle information for Y₁ axisindicating an axis after the Y₀ axis is rotated as much as Ψ2.
 5. Theinput system as claimed in claim 2, wherein the second computing unitcalculates the motion rotation angle information Φ by an equation asfollows: Φ(t)=a*t+b where, if t₁ denotes time just before the motions,t₂ denotes time just after the motions, a denotes [Φ(t₂)−Φ(t₁)]/(t₂−t₁),b denotes −a*t, +Φ(t₁), and coordinate axes for a navigation frame aredenoted as X₀, Y₀, and Z₀, then the Ψ denotes the rotation angleinformation for the Z₀ axis, the θ denotes the rotation angleinformation for the Y₁ axis indicating an axis after the Y₀ axis isrotated as much Ψ, and the Φ denotes the rotation angle information forthe X₂ axis indicating an axis after the X₀ axis is rotated as much as Ψand θ, respectively.
 6. The input system as claimed in claim 2, whereinthe second computing unit calculates the motion rotation angleinformation 0 based on an equation as follows: θ(t)=c*t+d where, if t₁denotes time just before the motions, t₂ denotes time just after themotions, c denotes [θ(t₂)−θ(t₁)]/(t₂−t₁), d denotes −c*t, +θ(t₁), andcoordinate axes are denoted as X₀, Y₀, and Z₀, then Ψ denotes therotation angle information for the Z₀ axis and the θ denotes therotation angle information for the Y₁ axis indicating an axis after theY₀ axis is rotated as much as Ψ.
 7. An input system based on athree-dimensional inertial navigation system and having an input partand a host device, and for detecting motion position informationcorresponding to three-dimensional motions of the input part andoutputting the detected motion position information to the host device,comprising: acceleration sensors for outputting motion accelerationinformation; a rotation angle information estimation-computing portionfor estimating motion rotation angle information Φ, θ, and Ψ based onacceleration information based on the gravitational accelerationseparated from the outputted motion acceleration information; aconversion-computing unit for calculating motion position informationbased on the estimated motion rotation angle information and theoutputted motion acceleration information; and an optimalplane-computing unit for projecting the motion position information ontoan optimal plane.
 8. The input system as claimed in claim 7, wherein therotation angle information estimation-computing portion includes: aseparation unit for separating acceleration information based on themotions of the input part itself and acceleration information based onthe gravitational acceleration from the outputted motion accelerationinformation based on a predetermined process; and a computing unit forcalculating the motion rotation angle information through apredetermined computing process based on the acceleration informationbased on the separated gravitational acceleration.
 9. The input systemas claimed in claim 8, wherein the predetermined process for separatingthe acceleration information based on the gravitational accelerationfrom the motion acceleration information is to pass the motionacceleration information through a low-pass filter.
 10. The input systemas claimed in claim 8, wherein the computing unit calculates the motionrotation angle information Φ based on an equation as follows:$\Phi = {\tan^{- 1}\left( \frac{A_{by}}{A_{bz}} \right)}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(by) denotes acceleration information for the Y axisand A_(bz) denotes acceleration information for the Z axis, and, ifcoordinate axes for a navigation frame are denoted as X₀, Y₀, and Z₀, Tdenotes rotation angle information for the Z₀ axis, θ denotes rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ, and Φ denotes rotation angle information for an X₂indicating an axis after the X₀ is rotated as much as Ψ and θ,respectively.
 11. The input system as claimed in claim 8, wherein thecomputing unit calculates the motion rotation angle information θ basedon an equation as follows:$\theta = {\tan^{- 1}\left( \frac{A_{bx}}{\sqrt{A_{by}^{2} + A_{bz}^{2}}} \right)}$

where, if coordinate axes for the body frame are denoted as X, Y, and Z,A_(bx) denotes acceleration information for the X axis, A_(by) denotesacceleration information for the Y axis, A_(bz) denotes accelerationinformation for the Z axis, and if coordinate axes for a navigationframe are denoted as X₀, Y₀, and Z₀, Ψ denotes rotation angleinformation for the Z₀ axis and θ denotes rotation angle information fora Y₁ axis indicating an axis after the Y₀ is rotated as much as Ψ.
 12. Atrajectory estimation method for an input system based on athree-dimensional inertial navigation system and having an input partand a host device, and for detecting motion position informationcorresponding to three-dimensional motions of the input part andoutputting the detected motion position information to the host device,comprising: (a) outputting motion acceleration information, pre-motionacceleration information, and post-motion acceleration information justafter the motions; (b) estimating motion rotation angle information Ψ,θ, and Ψ through a predetermined computing process based on theoutputted pre-motion acceleration information and post-motionacceleration information; (c) calculating the motion positioninformation based on the estimated motion rotation angle information andthe outputted motion acceleration information; and (d) projecting themotion position information onto an optimal plane.
 13. The trajectoryestimation method as claimed in claim 12, wherein the step (b) includes:(b1) calculating pre-motion rotation angle information Φ1, θ1, and Ψ1and post-motion rotation angle information Φ2, θ2, and Ψ2 through apredetermined computing process based on the outputted pre-motionacceleration information and post-motion acceleration information; and(b2) calculating the motion rotation angle information through apredetermined computing process based on the calculated pre-motionrotation angle information and post-motion rotation angle information.14. The trajectory estimation method as claimed in claim 13, wherein thestep (b1) calculates the pre-motion rotation angle information Φ1 andthe post-motion rotation angle information Φ2 based on equations asfollows: $\begin{matrix}{{{\Phi 1} = {\tan^{- 1}\left( \frac{A_{by1}}{A_{bz1}} \right)}};} \\{{\Phi 2} = {\tan^{- 1}\left( \frac{A_{by2}}{A_{bz2}} \right)}}\end{matrix}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(by1) and A_(by2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Y axis,respectively, and A_(bz1) and A_(bz2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Z axis,respectively, and, if coordinate axes for a navigation frame are denotedas X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote the pre-motion rotation angleinformation and the post-motion rotation angle information for the Z₀axis, and θ1 denotes the pre-motion rotation angle information for a Y₁axis indicating an axis after the Y₀ axis is rotated as much as Ψ1, θ2denotes the post-motion rotation angle information for Y₁ axisindicating an axis after the Y₀ axis is rotated as much as Ψ2, Φ1denotes the pre-motion rotation angle information for the X₂ indicatingan axis after the X₀ axis is rotated as much as Ψ1 and θ1, respectively,and Φ2 denotes the pre-motion rotation angle information for the X₂ axisindicating an axis after the X₀ is rotated as much as Ψ1, θ2,respectively.
 15. The trajectory estimation method as claimed in claim13, wherein the step (b1) calculates the pre-motion rotation angleinformation θ1 and the post-motion rotation angle information θ2 basedon equations as follows: $\begin{matrix}{{{\theta \quad 1} = {\tan^{- 1}\left( \frac{A_{bx1}}{\sqrt{A_{by1}^{2} + A_{bz1}^{2}}} \right)}},} \\{{\theta \quad 2} = {\tan^{- 1}\left( \frac{A_{bx2}}{\sqrt{A_{by2}^{2} + A_{bz2}^{2}}} \right)}}\end{matrix}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(bx1) and A_(bx2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the X axisrespectively, and A_(by1) and A_(by2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Y axisrespectively, and A_(bz1) and A_(bz2) denote the pre-motion accelerationinformation and the post-motion acceleration information for the Z axisrespectively, and, if coordinate axes for a navigation frame are denotedas X₀, Y₀, and Z₀, Ψ1 and Ψ2 denote the pre-motion rotation angleinformation and the post-motion rotation angle information for the Z₀axis, and θ1 denotes the pre-motion rotation angle information for a Y₁axis indicating an axis after the Y₀ axis is rotated as much as Ψ1, andθ2 denotes the post-motion rotation angle information for Y₁ axisindicating an axis after the Y₀ axis is rotated as much as Ψ2.
 16. Thetrajectory estimation method as claimed in claim 13, wherein the step(b2) calculates the motion rotation angle information Φ by an equationas follows: Φ(t)=a*t+b where, if t₁ denotes time just before themotions, t₂ denotes time just after the motions, a denotes[Φ(t₂)−Φ(t₁)]/(t₂−t₁), b denotes −a*t, +Φ(t₁), and coordinate axes aredenoted as X₀, Y₀, and Z₀, then the Ψ denotes the rotation angleinformation for the Z₀ axis, the θ denotes the rotation angleinformation for the Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ, and the Φ denotes the rotation angle informationfor the X₂ axis indicating an axis after the X₀ axis is rotated as muchas Ψ and θ, respectively.
 17. The trajectory estimation method asclaimed in claim 13, wherein the step (b2) calculates the motionrotation angle information θ based on an equation as follows: θ(t)=c*t+dwhere, if t₁ denotes time just before the motions, t₂ denotes time justafter the motions, c denotes [θ(t₂)−θ(t₁)]/(t₂−t₁), d denotes −c*t,+θ(t₁), and coordinate axes are denoted as X₀, Y₀, and Z₀, then Ψdenotes the rotation angle information for the Z₀ axis and the θ denotesthe rotation angle information for the Y₁ axis indicating an axis afterthe Y₀ axis is rotated as much as Ψ.
 18. A trajectory estimation methodfor an input system based on a three-dimensional inertial navigationsystem and having an input part and a host device, and for detectingmotion position information corresponding to three-dimensional motionsof the input part and outputting the detected motion positioninformation to the host device, comprising: (a) outputting motionacceleration information; (b) estimating motion rotation angleinformation Φ, θ, and Ψ based on acceleration information based on thegravitational acceleration separated from the outputted motionacceleration information; (c) calculating motion position informationbased on the estimated motion rotation angle information and theoutputted motion acceleration information; and (d) projecting the motionposition information onto an optimal plane.
 19. The trajectoryestimation method as claimed in claim 18, wherein the step (b) includes(b1) separating acceleration information based on the motions of theinput part itself and acceleration information based on thegravitational acceleration from the outputted motion accelerationinformation based on a predetermined process; and (b2) calculating themotion rotation angle information through a predetermined computingprocess based on the acceleration information based on the separatedgravitational acceleration.
 20. The trajectory estimation method asclaimed in claim 19, wherein the predetermined process in the step (b1)is to pass the motion acceleration information through a low-passfilter.
 21. The trajectory estimation method as claimed in claim 19,wherein the motion rotation angle information Φ in the step (b2) iscalculated based on an equation as follows:$\Phi = {\tan^{- 1}\left( \frac{A_{by}}{A_{bz}} \right)}$

where, if coordinate axes of a body frame of the input part are denotedas X, Y, and Z, A_(by) denotes acceleration information for the Y axisand A_(bz) denotes acceleration information for the Z axis, and, ifcoordinate axes for a navigation frame are denoted as X₀, Y₀, and Z₀, Ψdenotes rotation angle information for the Z₀ axis, θ denotes rotationangle information for a Y₁ axis indicating an axis after the Y₀ axis isrotated as much as Ψ, and Φ denotes rotation angle information for an X₂indicating an axis after the X₀ is rotated as much as Ψ and θ,respectively.
 22. The trajectory estimation method as claimed in claim19, wherein the motion rotation angle information θ in the step (b2) iscalculated based on an equation as follows:$\theta = {\tan^{- 1}\left( \frac{A_{bx}}{\sqrt{A_{by}^{2} + A_{bz}^{2}}} \right)}$

where, if coordinate axes for the body frame are denoted as X, Y, and Z,A_(bx) denotes acceleration information for the X axis, A_(by) denotesacceleration information for the Y axis, A_(bz) denotes accelerationinformation for the Z axis, and if coordinate axes for a navigationframe are denoted as X₀, Y₀, and Z₀, Ψ denotes rotation angleinformation for the Z₀ axis and θ denotes rotation angle information fora Y₁ axis indicating an axis after the Y₀ is rotated as much as Ψ.